I managed to do it every time with shielding everything on pull. It still needs some Prayers of Healing towards the middle but you manage.

Apparently Discipline Priest does not like random damage at all. Not at all indeed. It likes it if the 'random' ability has a warning on who it goes to, but that's not really random for it. But if damage itself goes randomly somewhere instantly (e.g. here due to mediocre dpses or tanks) then hell.